WASHINGTON – Two airliners landed at Reagan National Airport near Washington without control tower clearance because the air traffic supervisor was asleep, safety and aviation officials said Wednesday.

The supervisor — the only controller scheduled for duty in the tower around midnight Tuesday when incident occurred — had fallen asleep, said an aviation official, who spoke on condition of anonymity.

The National Transportation Safety Board is gathering information on the occurrence to decide whether to open a formal investigation, board spokesman Peter Knudson said.

The pilots of the two commercial planes were unable to reach the tower, but they were in communication with a regional air traffic control facility, Knudson said. That facility is in Warrenton, Va., about 40 miles from the airport.

Regional air traffic facilities handle aircraft within roughly a 50-mile radius of an airport, but landings, takeoffs and planes within about three miles of an airport are handled by controllers in the airport tower.

After pilots were unable to raise the airport tower by radio, they asked controllers in Warrenton to call the tower, Knudson said. Repeated calls to the tower went unanswered, he said.

The planes involved were American Airlines flight 1012 and United Airlines flight 628T, Knudson said.

The Federal Aviation Administration released a statement confirming the incident.

“The FAA is looking into staffing issues and whether existing procedures were followed appropriately,” spokeswoman Laura Brown said in an email.

It’s unlikely the safety of the planes was at risk since the pilots would have used a radio frequency for the airport tower to advise nearby aircraft of their intention to land and to make sure that no other planes also intended to land at that time, aviation safety experts said.

At that time of night, air traffic would have been light, they said.